1. Field of the Invention
The invention relates to data communications and networking and in particular, the access and management of beacon periods in superframes of distributed wireless networks.
2. Description of the Related Art
Generally, IEEE 802.11 based and other wireless networks require access points to coordinate and control medium access of devices in the network for wireless services. Services are interrupted or disabled in such networks when devices or access points move away from each other, when access points malfunction, or when access points do not coordinate among themselves, which is typically the case. Recently, a new generation of distributed wireless networks using high-speed, short-range ultra-wideband technology has been proposed by Multiband OFDM Alliance (MBOA) or WiMedia Alliance that does not require any existing infrastructure (such as access points) for communication. These networks can provide data throughput of up to about 500 Mbps. Protocols are defined for devices in a distributed wireless network to detect other devices within their neighborhood and establish communication with them without having to go through access points. The basic architecture of the wireless network is defined by various specifications issued by WiMedia, such as “Distributed Medium Access Control (MAC) for Wireless Networks”, Draft 0.99, Oct. 14, 2005, which is incorporated herein by references in its entirety for all purposes.
Distributed wireless networks may be formed without a central coordinator like an access point to overcome those drawbacks. In such networks, devices transmit their beacons as means of coordinating their medium access. These beacons are transmitted periodically, or once every predetermined time interval called a superframe. The superframe is a periodic time interval for coordinating frame transmission between devices. The superframe includes a beacon period (BP) followed by a data period. The superframe may have a predetermined duration and is composed of several Medium Access Slots (MAS), each MAS having a duration. The superframe starts with a BP, which may include one or more MASs. The start of the first MAS in the BP is referred to as the beacon period start time (BPST). The BPST can be defined by a device operating in a wireless network.
Beacons are transmitted in BPs located at the beginning of each superframe. Because the number of devices actively communicating in the network and hence in need of transmitting a beacon varies, it is desirable to have BPs that expand or contract in response to corresponding increase or decrease in the number of active devices so that the remaining period in the superframe can be maximized for data communication, which results in maximization of channel utilization. However, issues arise when BPs are allowed to vary in length and some devices may transmit their beacons into the same time interval as other devices, thus garbling the beacons.
When a device is turned on, it scans one or more communication channels to search for beacons from other devices in its neighborhood and selects a channel for communication. If the device detects one or more beacons in the selected channel, then the device synchronizes its BPST to that defined by the existing beacons in the selected channel and joins the group of devices having the same BPST. This group of devices is referred to as the beacon group (BG). These are logical groups of devices formed around each device to facilitate contention free frame exchanges between devices. If the device does not detect one or more beacons in the selected channel, then the device creates its own BP and sends a beacon on the selected channel to inform other devices that may later communicate in the selected channel.
Each device operates in a dynamic environment and has capability to dynamically change the channel in which it operates without requiring either user intervention or causing the disruption of communications with its peers. Similarly, devices in each BG can modify their BPs to adapt to the dynamic environment around them. Therefore, there is a need for a system and method to effectively access and manage BPs in a distributed wireless network.